Among articles used as earthquake proofing supports for decreasing acceleration to be inputted into structures and various apparatuses is a laminated rubber support comprising rigid plates and rubber-like elastic plates alternately laminated to each other.
Such laminated rubber support, as shown in FIG. 14, has a construction in which rigid plates 1 and rubber-like elastic plates 2 are alternately laminated to each other to form a laminate 3 and the latter is centrally formed with a vertically extending cylindrical hollow portion 4. Also known is a laminated rubber support of the peripherally constrained type in which a cylindrical viscoelastic body or plastic body 5 is fitted in the cylindrical hollow portion 4 of the laminate 3 as shown in FIG. 15.
In use, such laminated rubber supports having that construction are interposed between a superstructure, such as a building or floor, and a foundation or concrete slab, with attachment plates (not shown) attached to the uppermost and lowermost rigid plates 1 of each laminate.
When an earthquake or various vibrations occur, these laminated rubber supports decrease input acceleration by their tensile and compressive deformations in the vertical direction and shearing deformation in the horizontal direction to insulate buildings, various apparatuses and artistic handicrafts from earthquakes and various vibrations, thereby protecting them against earthquakes and various vibrations.
As for the performance of the laminated rubber supports, the stability of the laminated rubber support with respect to variations in vertical load depends largely on the inner diameter of the rigid plates 1 of the laminate 3. In the case of the laminated rubber support shown in FIG. 14, an increase in the inner diameter makes it possible to provide an earthquake proofing support whose vertical spring constant is lower (the earthquake proofing performance and vibration preventing performance are better) and saves the amount of rubber material to be used and thus lowers the cost of material. However, if the inner diameter is increased, the laminated rubber support tends to buckle even under a small amount of deformation when it is subjected to horizontal shearing deformation. That is, the size of the inner diameter has opposite effects on the vertical spring constant and the buckling performance. In the case of the laminated rubber support of the peripherally constrained type (see FIG. 15) in which a cylindrical viscoelastic body or plastic body 5 is fitted in the cylindrical hollow portion 4 of the laminate 3, if the inner diameter is decreased in order to improve the stability with respect to variations in vertical load upon horizontal great deformation, the volume of the viscoelastic body or plastic body 5 is decreased, making it impossible to obtain the required amount of attenuation. In such a laminated rubber support, the size of the inner diameter of the rigid plates 1 of the laminate 3 has opposite effects on the attenuation performance and the buckling performance; thus, it influences the two performances in opposite manners.
In designing the laminated rubber support described above, the inner diameter of the rigid plates 1 of the laminate 3 has been empirically determined through lack of appropriate means for determining it; thus, in the existing circumstances, there is no method of appropriately designing laminated rubber supports.
More particularly, it has been impossible to design a laminated rubber support superior in earthquake proofing performance and vibration preventing performance in the vertical direction, having a high buckling surface pressure and an appropriate inner diameter. Particularly in the case of the laminated rubber support having a viscoelastic body or plastic body fitted in the cylindrical hollow portion 4 of the laminate 3, the design of a laminated rubber support which highly attenuates under design conditions and which has the highest bucking surface pressure has not been definite.
Accordingly, the present invention, which is proposed in view of the above problems, is intended to disclose appropriate means for universally determining the inner diameter of the rigid plates of the laminate and to provide a laminated rubber support having an appropriate shape and a method of designing the same.